Quantifying Fine Sediment Sources in the Northeast Branch of the Anacostia River, Maryland, Using Trace Elements and Radionuclides

Abstract

Fine sediment sources were characterized in an urban watershed, the Northeast Branch of the Anacostia River, which drains to the Chesapeake Bay. Concentrations of 63 elements and two radionuclides were measured in possible sediment sources and suspended sediment collected at the watershed outlet during storm events. Methodology for selecting tracers was developed so the sediment fingerprinting method could effectively determine the relative quantity of sediment contributed by each source to the suspended fraction. The amount of enrichment of trace elements in sediment sources and suspended sediment was determined by calculating enrichment ratios, which are ratios of the normalized concentration of elements in the sample relative to their average normalized concentration in the Earth's upper continental crust. Streambanks contributed the highest relative quantity of sediment in the fall and spring while upland areas contributed mostly during winter. Street residue contributed 12% on average and was the source most concentrated in anthropogenically enriched elements.